The invention relates to production of reflective bodies such as road markers, and more particularly to the molding of a reflective body having "retroreflective" angled facets at its back surface for reflecting back light passing into the reflective body from the front.
Road markers having reflective features are well known. Generally, these are molded of relatively rigid plastics such as polyethylene, polyproplene, polycarbonates, or acrylic material. Taillight lenses for automobiles have been similarly produced.
These reflectors and reflective markers have often included so called "retroreflective" back surfaces comprising a multiplicity of angled facets, one such configuration being cube corners. See, for example, U.S. Pat. Nos. 3,684,348 and 3,810,804 (both to W. P. Rowland). See also U.S. Pats. Nos. 3,215,039, 3,450,459, 3,716,445, 3,785,719 and 3,851,947 for other retroreflective or reflex reflectors of various geometries.
It is also known to fabricate certain roadway markers of flexible urethane material, as disclosed in my earlier U.S. Pat. No. 4,297,051. That patent was directed to a deformable roadway marker having a dome-shaped top which would deform elastically downwardly when struck by a snowplow blade, then return to the domed configuration, thereby permitting the use of raised reflective "bumps" on a road surface in geographical areas experiencing snow in winter. Urethane is an excellent material for this purpose because of its flexibility, toughness, clarity and consisting in physical properties through wide ranges of temperature.
In my earlier patent, I disclosed the use of a strip or body of reflective material placed in the mold and captured into the molded urethane marker between its top and bottom surfaces, so that light from automobile headlights would pass through the light-transmitting surface of the marker and be reflected back out by the strip of reflective material inside.
Prior to the present invention, there has not been any practicable way for achieving the molding of retroreflective angled facets on the back surface of a flexible urethane marker, although this has been achieved with other, more rigid plastics. In forming molded retroreflective reflector articles from hard plastics, such as used in automotive tail lenses, it has been common practice to use a mold piece carrying reflex facets, the mold piece being held within the mold when the plastic material is injected.
Urethane is an adhesive, very tenacious material as it hardens, and when it is molded the mold must be coated with a release agent in order to successfully remove the urethane article from the mold. However, known release agents generally will destroy the effect of multiple-facet retroreflective surfacing molded on a urethane article. This is because the optic surface of the reflective facets will be clouded by these mold releasing agents. The facets must be precisely planar and uniform, and such surface irregularities will cause diffusion of the light striking the facets, rather than the precisely directed reflection needed in such a marker.
In general, optical plastic parts cannot be molded using a release agent, and urethane, a particular plastic, requires the use of a releasing agent or something which functions as a releasing agent.
No practicable system or method was available for molding reflex facets on a flexible urethane reflective article, prior to the present invention described below.